1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to compensating signal distortion caused by noise and, more particularly, to compensating signal distortion caused by non-zero mean random noise of an imaging device to improve picture quality.
2. Description of the Related Art
Imaging devices convert light into an electric signal corresponding to an image, and include complementary metal oxide semiconductor (CMOS) imaging devices and charge coupled device (CCD) imaging devices. An imaging device is required to generate an electric signal ideally proportional to the illuminance of light input thereto; however, various noise is added when the light is converted into the electric signal. This noise includes dark current noise, kTC noise, fixed pattern noise, etc.
Dark current noise is thermal noise proportional to temperature and deteriorates the picture quality of an image when the image is obtained with a low illuminance. kTC noise is generated according to various switching pulse signals used to drive a CMOS camera or a CCD camera. Fixed pattern noise is generated when a CMOS imaging device or a CCD imaging device includes a defect pixel. The fixed pattern noise is caused by non-uniformity generated due to various causes in a CMOS manufacturing process or a CCD manufacturing process and appears as white spot defect, black spot defect, line defect, banded spot defect and sensitive speck. The aforementioned noise is added to charges photo-electric-converted by an imaging device and accumulated to deteriorate picture quality.
FIG. 7 is a graph for explaining noise generated according to illuminance of light input to an imaging device. Referring to FIG. 7, a small dynamic range and a relatively high noise level compared to the magnitude of a signal at a low illuminance become problems in the imaging device. When the illuminance of light input to the imaging device is high, that is, when an image-capturing environment is bright, noise generated in the imaging device is considerably smaller than the quantity of charges photo-electric-converted by the imaging device and accumulated, and thus picture quality is not largely deteriorated. However, when the image-capturing environment is dark, noise such as fixed pattern noise, dark current noise and kTC noise become relatively larger compared to the quantity of charges photo-electric-converted by the imaging device and accumulated, and thus picture quality is severely deteriorated.